Reproductive biology of the commercial sea cucumber Holothuria fuscogilva in the Solomon Islands

 Reproduction of Holothuria fuscogilva (Selenka, 1867) in the Solomon Islands was investigated over a 4 yr period (1994 to 1998) by macroscopic and microscopic examination of the gonad tubules, the gonad index (GI) method, histological examination of gametogenesis, and spawning-induction trials. The gonad consisted of numerous tubules that dominated the coelom of gravid specimens. New tubules appeared in March, and grew in size and extent of branching until they reached their maximum size and maturity in August. Spawning occurred from August to October, with the majority of gametes released during October, although it was only partial in many individuals. After spawning, the tubules appeared wrinkled and resorbed into the gonad basis. A five-stage gonad maturity scale based on the macroscopic appearance of the gonad tubules corresponded with discrete stages of gametogenesis identified by histology. Gametogenesis was initiated in mid-March, with oogenesis and spermatogenesis occurring in parallel, followed by the growing stage (May to July) which was marked by active gamete development. Successful induction of spawning during the breeding period corroborated the GI and histological data. The uniform growth of gonad tubules indicated that H. fuscogilva in the Solomon Islands does not conform to the progressive tubule recruitment model described for other holothurians. An important application of this study is that the appearance of gonad tubules, removed by biopsy, can be used to determine the gonad condition of wild adults or captive broodstock. Received: 28 June 1999 / Accepted: 8 March 2000     

Reproduction of the commercial sea cucumber Holothuria scabra (Echinodermata: Holothuroidea) in the Solomon Islands

Over a 3-year period (1996-1998), reproduction of the commercial sea cucumber Holothuria scabra (Jaeger, 1833) was investigated in the Solomon Islands to determine the spawning pattern and whether gametogenesis is continuous or seasonal. The gonad consisted of a single cohort of tubules that developed uniformly. Macroscopic examination of the gonads revealed that mature gametes were present throughout the year. Individuals with gonads at different stages of maturity were present in most samples. Partly spawned gonads were prevalent in females, whereas mature gonads were prevalent in males. The time at which the peak gonad index was recorded differed among years. Although gametogenesis was continuous, with a potential for prolonged gamete release, a period of enhanced spawning occurred during the dry season, from September to December. Maximum gonad indices were reached prior to and during this period of enhanced spawning. Histology revealed that gametogenesis reinitiated in partly spawned gonads, resulting in the presence of gametes at different stages of development in the gonad. The uniform growth of gonad tubules indicated that H. scabra does not conform to the progressive tubule recruitment model described for holothurian oogenesis. Continuous reproduction in H. scabra and prolonged availability of mature gametes would facilitate use of this species for aquaculture.     

Manipulation of food and photoperiod promotes out-of-season gametogenesis in the green sea urchin, Strongylocentrotus droebachiensis: implications for aquaculture

Green sea urchins, Strongylocentrotus droebachiensis OF Müller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development of nutritive phagocytes, the volume fraction (V _v) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% V _v. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied a V _v of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population dynamics may be useful in aquaculture applications. Received: 21 February 1997 / Accepted: 3 June 1998     

Assessing reef fish assemblage structure: how do different stereo-video techniques compare?

Measures of fish abundance, assemblage composition and length were compared when sampled by baited remote underwater stereo-video (stereo BRUV) and diver-operated stereo-video transects (stereo DOV) at the Houtman Abrolhos Islands and Ningaloo Reef. Species richness counts were 40% higher on stereo BRUV than stereo DOV. Stereo BRUVs also recorded a greater number of large-bodied targeted species in higher abundance than stereo DOV (e.g. Lethrinus nebulosus, Plectropomus leopardus) at the Houtman Abrolhos and at Ningaloo Reef. Many non-targeted species were also recorded in greater abundances on stereo BRUV than stereo DOV (e.g. Coris auricularis, Gymnothorax spp). Stereo DOV transects recorded a greater abundance of some small-bodied Pomacentridae, Labridae and Scaridae species than did stereo BRUV, particularly at Ningaloo Reef. This study demonstrates that choice of sampling technique for surveys of reef fish can lead to very different biological interpretations of fish assemblage structure.     

Reproductive periodicity in the euryalinid snake star Astrobrachion constrictum in a New Zealand fiord

The euryalinid snake star Astrobrachion constrictum (Farquhar), a normally deep-water species, exists within SCUBA diving range in New Zealand flords, and thus presents a unique opportunity for study. A population of A. constrictum in Doubtful Sound was investigated from February 1990 to July 1994 to determine the reproductive cycle. Unlike most ophiuroids, the gonads of A. constrictum are positioned along the aboral coelom in the proximal portion of the arms. The proximal 2 to 3 cm of the arms of individuals were thus removed on an approximately monthly basis for histological examination of the gonads. Image analysis was used to determine oocyte size-frequency distributions. A gonad index was calculated for each individual based on the ratio of cross-sectional area of the gonads to cross-sectional area of the arm. Maturity indices were calculated based on stage of development of the gonads of each individual. A. constrictum has a period of enhanced breeding activity in April–June, after which both the gonad and maturity indices decline. The increase in gametogenic activity during these months was correlated with rising sea temperature within the fiord. Although the females showed an annual pattern of gonad development, oogenesis was continuous throughout the year, with oocytes at different stages of development present in the gonads. Males also showed continuous spermatogenesis and, although the same annual pattern of gonad development was evident as seen in the females, it was less marked. The presence of females with large oocytes and ripe males throughout the study indicates that breeding in the Doubtful Sound population is prolonged, and possibly continuous, as found in many deep-sea ophiuroids.     

Gametogenesis of Pollicipes cornucopia (Cirripedia: Scalpellomorpha) in north-west Spain

The gametogenesis and gonad microanatomy of the stalked barnacle Pollicipes cornucopia (Leach) is described. An histological classification of gametogenic development is proposed for the firt time for a species of the Cirripedia. This species has an annual gametogenic cycle on the north-west Spanish coast. Spawning takes place mainly from March to September. Ovaries release gametes at least twice during the gametogenic cycle.     

Reproductive cycle of two populations of Ophionereis schayeri (Ophiuroidea) in New South Wales

Reproduction of two populations of Ophionereis schayeri (Müller and Troschel) in New South Wales was investigated from November 1991 through January 1993. The reproductive cycle was documented by histological examination of the gonads and by image analysis to determine the oocyte size-frequency distributions. Both populations of O. schayeri were mature in December and January and had a major summer spawning period between January and February. Thereafter, the condition of the gonads exhibited interindividual variability, with asynchronous low-intensity gamete release through August. O. schayeri has the potential to spawn for up to 8 mo of the year. This breeding pattern with synchronous spawning in summer and asynchronous gamete release through winter was similar in both populations. During autumn and winter, the gonads contained developing gametes and advanced gametes ready for spawning. The eggs spawned by O. schayeri during these seasons started their growth during the previous spring vitellogenic period, and continued to grow through summer. Upon reaching full size, they were stored for spawning outside the main breeding period. Spring is marked by increased spermatogenic and vitellogenic activity followed by maturation and spawning. Throughout their development, the oocytes of O. schayeri are surrounded by a follicle consisting of periodic acid-Schiff-positive (PAS+) haemal fluid and PAS+ yolk by the oocytes. In the testes, the haemal sinus projects into the centre of the spermatocyte columns, thus appearing to play a nutritive role in support of both oogenesis and spermatogenesis. Late vitellogenic oocytes of O. schayeri are firmly anchored to the germinal epithelium by an attachment complex consisting of specialised attachment cells and basophilic strands that radiate between the oolemma and the nucleus. Spawning is associated with rupture of the follicles, which remain as prominent, empty U-shaped profiles in the ovaries. O. schayeri produces copious numbers of 200 m-diam oocytes, suggesting that this species is a broadcast spawner and that it has a modified ophiopluteus or vitellaria larva.     

Introduction of the northern Pacific asteroid Asterias amurensis to Tasmania: reproduction and current distribution

The northern Pacific asteroid Asterias amurensis (Lütken) has been recently introduced to Tasmania and is now well-established in east and southeast Tasmania. This sea star is conspicuous throughout the Derwent River estuary and is particularly abundant in the Hobart port area. Reproduction of two populations of A. amurensis at Sullivans Cove and at Sandy Bay was investigated from August 1993 to October 1994 by gonadal histology and measurement of the gonad index (GI). An intense period of vitellogenic and spermatogenic growth started in April, with the breeding condition reached by June. In 1994, peak GI was recorded at Sullivans Cove in July and at Sandy Bay in August. Although these data indicated that the Sullivans Cove population spawned before the Sandy Bay population, histological examination revealed that major spawning activity occurred in both populations from July onwards. In the early part of the breeding season, gametogenesis proceeded in parallel with spawning, with released gametes being replaced by continual gametogenesis. Maintenance of a higher GI during the early part of the breeding season at Sandy Bay was due to prolonged gametogenic replacement at this site. Spawning continued to October 1994, resulting in a sharp decline in the GI. The cyclic expansion and regression of the genital haemal sinus coincident with germinal proliferation and growth, respectively, support the contention that haemal fluid provides nutrients for gametogenesis. In Tasmania, A. amurensis experiences temperature and photoperiod regimes similar to those experienced by endemic populations of this species in the north Pacific. Comparison of reproduction of A. amurensis in Japan and Tasmania at similar latitudes shows that gametogenesis of the northern and southern populations is 6 mo out of phase. This phase shift provides evidence for photoperiodic regulation of gametogenesis in A. amurensis. The similar trend in sea-temperature regimes associated with the stages of gametogenesis in northern and southern populations suggests that temperature also plays a modulatory role. Based on the periodicity of reproduction and the ontogeny of A. amurensis, the planktotrophic larvae of this species would be expected to be in the plankton for several months from the end of winter through summer. Considering the highly fecund, dispersive life-history of A. amurensis, the southeast Tasmanian populations have considerable potential to serve as a seed source for establishment of new populations of this asteroid elsewhere in Tasmania and in mainland Australia. Received: 18 October 1996 / Accepted: 22 October 1996     

Cuvierian tubules of the holothuroid Holothuria forskali (Echinodermata): a morphofunctional study

Quiescent Cuvierian tubules of Holothuria forskali (Delle Chiaje, 1823) have a pseudostratified mesothelium made of ciliated cells that cover elongated cells containing lipoproteie granules. Together these cells form conspicuous transversal folds that penetrate the underlaying connective tissue. Circular and longitudinal muscle cells occur under the tips of the mesothelial folds. These cells are presumably myoepithelial cells; they divide the connective tissue into a thin outer layer (where collagen fibers are directed perpendicularly to the tubule long axis) and a thick inner layer (where collagen fibers are arranged in helices parallel to the tubular long axis). Nerve processes are associated with the longitudinal muscles; they also occur between the spirally arranged collagen fibers. A spiral nerve runs along the tubules; it innervates the circular muscles. The tubule lumen is narrow with a highly convoluted limiting epithelium. Epithelial cells are not ciliated; they have basal processes that contain enlarged spherules including mucosubstances and proteins. While having the same diameter as quiescent tubules, elongated tubules have a much thiner wall surrounding an enlarged cylindrical lumen. The mesothelium has no adluminal cells and consists of unfolded granular cells. In contact with a solid surface, granules become a sticky secretion. Longitudinal muscle fibers disintegrate and circular fibers form conspicuous rings along the tubules. Collagen helices still occur, but are considerably elongated and flattened. Inner epithelial cells dissociate from each other and typically lack basal processes and spherules, the latter being secreted into the lumen of elongating tubules. Discharge of Cuvierian tubules results from tubule expulsion and elongation. Tubule expulsion is triggered by the opening of the anus of a contracted holothuroid and results from the rupture of the cloaca with subsequent expulsion of coelomic fluid. Tubule elongation results both from the mechanical stimulation of the tubule sphincter by hydrostatic pressure and the entry of water into the tubule. Mechanical stimulation of the sphincter results in a rapid contraction of the circular muscles that causes the disintegration of adluminal cells, the unfolding of granular cells and the stretching of inner epithelial cells. Entry of water immediately follows sphincter stimulation and complete tubule elongation. Water pressure causes the irreversible elongation of collagen helices, which results both in a considerable thinning of the tubule wall and the formation of enlarged water-filled lumen. It is suggested that slippage of collagen fibers in elongating tubules is nervously mediated.     

Defensive mechanisms and ecology of some tropical holothurians

The ecology, defensive behavior and toxicity of three species of reef flat holothurians (Actinopyga mauritiana, Holothuria atra and Holothuria difficilis) were studied at Eniwetok Atoll, Marshall Islands. The average diurnal population density of H. difficilis ranged from 1.4 to 32 holothurians/900 cm²; resting respiratory rates (0.05 ml O₂/g wet wt/h) were comparable during day and night; nourishment in H. difficilis may be primarily from bacteria and foraminifera in which about 2% of the dry weight of sediment consumed is utilized, and the species probably passes at least 3 g dry wt of sediment/m²/day (>1 kg/m²/year). A fundamental difference in energy flow is suggested: considerably more energy is passed from benthic algae to grazing and browsing fishes to predatory fishes on coral reefs whereas, in extra-tropical latitudes, more energy is shunted from benthic algae to invertebrates to predators. The effects of holothurin leading to death in fishes are irreversible. Holothuria difficilis is best protected from predation. Its body wall is toxic and it can accurately eject Cuvierian tubules, which are also toxic. The discharge of tubules was regulated by a circadian rhythm in May. Studies on holothurians and sponges suggest that many exposed coral reef invertebrates have evolved effective defensive mechanisms in association with high intensity predation.Supported by A.E.C. Contract AT (29-2)-226 with the University of Hawaii.     

Movements of whale sharks (Rhincodon typus) tagged at Ningaloo Reef, Western Australia

Whale sharks (Rhincodon typus Smith) aggregate seasonally (March–June) to feed in coastal waters off Ningaloo Reef, Western Australia. Pop-up archival tags were attached to 19 individuals (total lengths 4.5–11.0 m) at this location in early May of 2003 and 2004 to examine their horizontal and vertical movements. The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef. They used both inshore and offshore habitats and made extensive vertical movements, occasionally to a depth of at least 980 m. Frequent up-and-down movements, diel vertical migration, and crepuscular descents were evident in the depth records. The sharks experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.     

Effects of temperature,nutritive and metal stressors on the reproductive biology of Mytilus edulis

Experimental observations suggest that the gametogenic cycle of Mytilus edulis from Swansea Bay, South Wales (U.K.) is adversely modified by the combined effects of temperature, nutritive and sublethal metal-induced stress. During low temperature stress, oogenesis remained in the vegetative stage and vitellogenesis only commenced when temperatures were raised to ambient levels. Copper was the most toxic metal, although its uptake was slowest. A concentration of 0.05 mg l^-1 of this metal proved lethal at ambient temperatures, although at low temperatures there was no mortality. Copper suppressed both the growth of young oocytes and vitellogenesis in larger oocytes. Zinc was less toxic than copper, although this also inhibited oocyte development and resulted in severe lysis of gametes. Cadmium was the least toxic of the three metals studied and suppressed gametogenesis only in the initial stages of gonad development. The low toxicity of cadmium to gametogenesis may be a result of its high solubility and its possible storage in the digestive gland.     

The annual reproductive cycle of the holothurian Aslia lefevrei (Dendrochirota: Echinodermata)

The dendrochirote holothurian Aslia lefevrei (Barrois) is locally and densely aggregated (>70 individuals m^-2) in Galway Bay, on the west coast of Ireland. It has a discrete, relatively short breeding period from the end of February to the beginning of April, with peak activity in March. The sexes are separate and the single gonad, consisting of numerous tubules (100 to 800), lies in the anterior coelom. Both gonad index values and histological observations indicate that gametogenesis resumes in June/July after a brief post-spawned resting period. Little oocyte growth and sperm production occurs over the warm summer months when the holothurian is actively feeding. Gonad index values, however, increase rapidly during this period and reach high values by early winter without concomitant increases in maturity indices. This is subsequently followed by slight reductions in the gonad indices, before reaching peak values in February. It is suggested that this is probably due to the initial build-up and subsequent assimilation of storage products in the gonad, the development of gametogenic products and the frequent assimilation thereafter of unwanted ova. Spawning generally takes between 5 and 60 min, with the entire contents of the gonad rarely being shed in a single release. During this process, the holothurian raises its anterior end and, with the extended tentacles close together, emits a stream of gametes from the genital pore in the mid-dorsal line. Laboratory experiments and general observations indicate that increased temperature and low light levels may influence spawning behaviour.Contribution No. 248 to the School of Marine Sciences, University College Galway, Ireland     

Reproductive biology of the holothurians from the major communities of the New Caledonian Lagoon

The reproductive biology of nine species of aspidochirote holothurians from the major communities of the New Caledonian lagoon has been analysed. The data were obtained from monthly sampling from 1978 to 1982 of their populations on reef slopes and passes for Holothuria nobilis, H. fuscogilva, H. fuscopunctata and Thelenota ananas, in the inner lagoon for Stichopus variegatus, H. scabra and H. scabra versicolor and on reef flats for Actinopyga mauritiana, A. echinites and H. atra. The morphology and anatomy of the gonads and their annual cycle are described. The reproductive cycles, composed of the five phases of gonad growth, maturing, spawning, post-spawning and resting, were determined from the changes in the sexual stages, the gonad indices and the percentage of indeterminate sex. Three main reproductive patterns are recognized, annual cycles with spawning occurring during the warm season or during the cool season and a semiannual cycle. Other population parameters, such as the size of the mature oocytes, the mean size of the individuals at first sexual maturity, and absolute and relative fecundities were calculated and related to the mean size of the species, the taxonomy and the ecology. The reproductive strategies of the species show a gradient that is probably related to the stability of the biotopes, with smaller species living in the more intrable outer reef flats and larger species in deeper lagoon floors.     

Reproductive strategies of two deep-sea gastropod species from the Porcupine Seabight (Northeast Atlantic)

Two species of small gastropods (<6 mm in length), Amphissa acutecostata (Philippi, 1844) and Gymnobela subaraneosa (Dautzenberg and Fischer, 1896), widely distributed in the northeast Atlantic, were found in large numbers in the Porcupine Seabight (Northeast Atlantic). Except for some aspects of taxonomy and distribution, as well as some data on larval development, the biology of these species is unknown. This study describes basic aspects of the life-history strategies of both species. Histological studies showed that oocyte and sperm development in both species was similar to the gametogenetic patterns observed in other deep-sea gastropods. In females, oogonia proliferated in the germinal epithelium and developed into previtellogenic oocytes (30–40 m), which grew into vitellogenic primary oocytes. Vitellogenic oocytes were covered by a thin layer of follicle cells involved in the vitellogenic processes. The maximum size for mature oocytes was 99.06 m for A. acutecostata and 114.82 m for G. subaraneosa. In A. acutecostata most of the volume of the ovary was occupied by previtellogenic and early vitellogenic oocytes, whereas in G. subaraneosa most of the volume was filled by large vitellogenic oocytes. Both species showed quasi-continuous production of oocytes. The oocyte size-frequency diagrams suggested a continuous release of a small number of oocytes throughout the year for A. acutecostata, and asynchronous periodic spawning events for G. subaraneosa. Gonad development and gametogenesis could be strongly affected by presence of parasites in one of the populations of G. subaraneosa.Communicated by J.P. Thorpe, Port Erin     

Reproductive biology and biochemical composition of the brooding echinoid <Emphasis Type="Italic">Amphipneustes lorioli</Emphasis> on the Antarctic continental shelf

The bathyal West Antarctic Peninsula (WAP) shelf experiences intense seasonal variability in primary production, with summer phytoplankton blooms yielding intense pulse of phytodetritus to shelf sediments. Echinoderms form a conspicuous proportion of the deposit-feeding megabenthos on the shelf and of these Amphipneustes lorioli was the most abundant irregular echinoid. To explore the reproductive response of A. lorioli to this seasonal production cycle, A. Lorioli was sampled at one location on the WAP shelf during four separate cruises between March 2000 and March 2001. Reproductive patterns were determined by histological analyses of gonad tissue, and elemental (CHN) analyses were used to estimate the nutritional and energetic status of the body tissues. Histological analysis of the brooding echinoid A. lorioli suggested a quasi-continuous gametogenic pattern in both the ovaries and the testes. Biochemical analysis of the gonads and the gut tissues were consistent with a continuous gametogenic cycle, showing no significant changes in the biochemical composition of the tissues among seasons. Size-frequency distributions of the embryo and juvenile echinoids within the adults’ brood pouches revealed a synchronous recruitment of embryos and juveniles in specific cohorts between different adult specimens. Whilst this occurrence of different cohorts of the developing brood may be an adaptation to limited brood space, there may also be an external factor influencing the synchrony between adult individuals. Nonetheless, a continuous gametogenic cycle and the lack of seasonal variation in the biochemical composition of gonad and gut tissues suggest that this deposit-feeding irregular urchin is exploiting a persistent sediment food bank in WAP shelf sediments throughout much of the year.     

Gonadal cycle in an<Emphasis Type="Italic"> Adelomelon brasiliana</Emphasis> (Neogastropoda: Volutidae) population of Buenos Aires province,Argentina

The reproductive season of the Adelomelon brasiliana population of Mar del Plata extends from September to April (austral spring and summer), showing synchronisation with water temperature. Adult gonad state is related to shell-free wet mass. Oocytes reach 200 m in diameter before spawning. In autumn, a resting phase begins, when no new oocytes develop and the non-spawned ones undergo reabsorption. Gonadic development begins during the early winter, when new previtellogenic oocytes can be observed through histology. The long reproductive season would increase the ability of the species to recover from harvesting.Communicated by O. Kinne, Oldendorf/Luhe     

Can photoperiod manipulation affect gonad development of a boreo-arctic echinoid (Strongylocentrotus droebachiensis) following exposure in the wild after the autumnal equinox?

A laboratory experiment was conducted in the winter of 2003–2004 to assess the effect of varying photoperiod regime on consumption rate, assimilation rate, absorption efficiency, and gonad development of the green sea urchin, Strongylocentrotus droebachiensis. Adult individuals were collected from the wild after they had been exposed to the ambient autumn photoperiod cue (which is the extraneous trigger thought to elicit gametogenesis in this species) and placed at ambient temperature for 12 weeks under five different photoperiod regimes: (1) 24 h light:0 h dark=“0D”, (2) 16 h light:8 h dark=“8D”, (3) 8 h light:16 h dark=“16D”, (4) 0 h light:24 h dark=“24D”, and (5) ambient photoperiod (range: 10.50–15.25 h dark). Urchins in these five treatments were fed ad libitum with bull kelp, Nereocystis luetkeana. A sixth treatment consisted of starved individuals held under 0D conditions. Various gonad factors including gonad index, percent gonad water, gonad colour (CIE lightness or L*, CIE hue or a*, and CIE chroma or b*), percent area occupation of the gonad by various cell types (nutritive phagocytes, spermatozoa, and secondary oocytes/ova), and stage of development were assessed at the beginning of the experiment and at weeks 4, 8, and 12 of the study. Consumption and assimilation rates were assessed at weeks 4 and 12 and absorption efficiency at week 12 of the experiment. Urchins were predominantly in the growing and premature stages at the beginning of the experiment, but by week 4 at least 20% of individuals in all treatments receiving food were classified as mature. Spawning occurred during all these treatments between weeks 4 and 8, as evidenced by significant decreases in spermatozoa and secondary oocytes/ova and a significant decrease in percent gonad water, but was not accompanied by major declines in gonad indices. Greater than 90% of individuals in all five of the fed treatments were in the recovering and growing stages at the end of the experiment. The 16D treatment had by far the greatest percentage of urchins in the growing stage. In contrast, individuals that were starved were predominantly in the mature stage at weeks 4, 8, and 12, with only ~30% reaching the spawning stage by the end of the experiment. Photoperiod significantly affected gonad indices at the termination of the experiment with gonad index being the highest in the 16D treatment; this was significantly greater than in the 8D and ambient treatments. Photoperiod did not significantly affect gonad percent water, gonad lightness, or gonad hue. Gonad chroma was significantly affected by photoperiod, urchins held under ambient conditions having significantly lower b* readings than individuals in any other treatment. Photoperiod had little or no affect on consumption rate, assimilation rate, or absorption efficiency. Thus, differences among treatments in regards to gonad index, gonad chroma, and stage of development cannot be attributed to variations in feeding, absorption, or assimilation. The results of this experiment indicate that once gametogenesis is initiated, photoperiod manipulation cannot prevent ultimate spawning. However, photoperiod regime can affect the rate at which urchins move through the various stages of the gametogenic cycle. Urchins placed on short days under artificial lighting (16D) moved through the spawning stage into recovering and growing stages the fastest. This photoperiod regime also produced the highest gonad index at the end of the experiment. Since the commercial urchin market prefers large gonads in the growing and premature stages (i.e. before the mature stage is reached and gonads start leaking sperm and eggs), short day-lengths under artificial lighting (16D) appear to be the best photoperiod conditions for optimizing marketability.     

The basics of acidification: baseline variability of pH on Australian coral reefs

Ocean acidification is one of the key threats facing coral reef ecosystems, but there are few estimates of spatial and temporal variability in pH among reef habitats. The present study documents levels of spatial variability in pH among coral reef habitats (9 to 10), among locations separated by 100’s km of latitude and between east (Great Barrier Reef, GBR) and west (Ningaloo Reef) coasts of Australia. Differences were found in pH between inshore and offshore waters along Ningaloo Reef (means 8.45, 8.53, respectively). Replicate assessments here ranged from 8.22 to 8.64. On the GBR, the range of values over all habitats and replicates was 0.39 pH units (7.98 to 8.37). There were minor but significant differences of 0.05 pH units between 5 consecutive days for habitats on average. Highest pH was recorded in filamentous algal beds maintained by the damselfish Dischistodus perspicillatus. Lowest pH was found in water extracted from sand-dwelling goby holes. While there were marked changes in pH over a 48-h sampling period among 4 habitats at Lizard Island (GBR), there was little evidence of a diel trend. Understanding how pH varies at scales that are relevant to organisms that live on shallow coral reefs is crucial for the design and interpretation of experiments that test the effects on organisms of the changes in water chemistry predicted to affect oceans in the future.     

The dual functions of sea urchin gonads are reflected in the temporal variations of their biochemistry

Fatty acid analyses are emerging as a powerful technique to probe trophic interactions between organisms. In this paper, the application of both this procedure and gonad index (GI) determination on two populations (intertidal and subtidal) of the echinoid Psammechinus miliaris is reported. The investigation spanned the 3-month spawning period of Scottish west coast populations. In both populations a progressive decrease in the GI was found, coupled with an increasing maturity stage (from mature to spent). Sexual maturation and decrease in GI was synchronous between the two populations. In conjunction, there were distinct changes in gonad biochemistry. Differences in the fatty acid composition of the gonad reflected the changes in sexual maturation. Mature males and females had significant differences in the fatty acid composition of their gonads, whereas post-spawned individuals showed no gender differences. Male urchins had higher levels of polyunsaturated fatty acids (PUFAs) compared to females, and there was a dramatic reduction in the fatty acids 22:6(n−3) and 20:5(n−3) with increasing maturity stage. Using multivariate statistical techniques, these changes in the fatty acid composition of the sea urchin gonad were linked to habitat related diet differences combined with gender differences. These changes in the fatty acid signatures clearly reflect the dual function of the gonad as both a nutrient store and a reproductive organ.